Process of vulcanizing neoprene



Patented June 25, 1946 UNITED STATES. PATENT OFFICE PROCESS OF VULCANIZ ING NEOPRENE James P. Nowlen, Wilmington, Del., and Maynard F. Torrence, Woods town, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 2, 1943,

Serial No. 477,772

16 Claims. 1

This invention relates to a process for vulcanizing neoprene (polymerized chloro-2-butadiene- 1, by the use of metallic salts of organic monocarboxylic acids the dissociation constant of which is less than 1.0 X

In the vulcanization of neoprene (chloro-2- butadiene-1,3) the stock is usually heated in the presence of certain metallic oxides with or without the addition of sulfur and usually in the presence of vulcanization accelerators. It has been found, however, that some stocks tend to prevulcanize during processing, extrusion or calendering, especially if the uncompounded polymer employed in the mix isnot recently prepared neoprene. The tendency of the stocks to prevulcanize is especially pronounced when organic" accelerators are employed. This condition is generally referred to as scorchiness, and results in a great loss of.time and material. Extensive research has therefore been carried out in an attempt to find some way, of retarding the rate of vulcanization at temperatures and under conditions normally employed in'the processing of the stock and yet which would not adversely affect the rate of vulcanization at the curing or "vulcanizing temperatures.

It is, therefore, an object of this invention to provide a process for vulcanizing neoprene (polymerized chloro-2-butadiene-1,3) in the presence of zinc oxide and magnesium oxide wherein the danger of .scorchiness is either minimized or polymerized chloro-2-butadiene-l,3 by employing vulcanization retarders, together with vulcanization accelerators and accelerator-activators whereby stocks are produced which are sufficiently safe at processing temperatures for commercial utilization and yet at the same time are active at the curing temperatures. A still further obcompletely eliminated. It is a further object of the invention to improve the vulcanization of 2 ject of the invention is to provide vulcanized 'po merized chIoro-Z-butadiene- 1,3 having improved properties.

We have found that the vulcanization in the presence of zinc oxide and magnesium bxide'ot polymerized chloro-2-butadiene-1,3 can be retarded by incorporating therein metallic salts oi. organic'mono-carbozwlic acids which have a dissociation constant of less than 1.0 X 10- These compounds have the property of retarding the rate of vulcanization of neoprene at processing temperatures of around 227 F. without retarding the rate of vulcanization at curing temperatures such as'a-bout 274 F. These compounds may be used alone or in conjunction with organic accelerators and accelerator-activators to produce neoprene stocks which exhibit excellent physical properties and show high resistance toward aging I and hightemperature deterioration as well as improved resiliency.

The following'table is given to show the dissoelation constant of some of the more common organic acids and the effectiveness of their salts in retarding the rate of vulcanization of neoprene.

The salts are classified as effective when they retard the rate of vulcanization at 227 F. but not Table II Phony] alpha'napbthylamine. Extra light calcined magnesia Channe carbon bl ck Zinc oxide Sodium acetata. Sodium caprylate Neoprene prepared according to the method described in U. S. P. 2,,173, Example 25, and stored five months.

. CURE: MIN. AT 222 F.

Modulus at 600%, lbalsq. in 650 200 250 Tensile strength, lbsJsq. in. 2, 050 775 625 Elongation at break (percent) 1, 210' 1,380 1, 235

CURE: so MINQAT 274 F.

Modulus at 000% lbs/sq. in

Tensile strength, lbs/sq. in Elongation at break (percent).- Hardness (Sh Btabillt testat 120 F No. oi ya to set up l Test not made.

I Method described by Larrlck, Rubber Age, Sept. 1940, p. 287.

As illustrated above, there is a marked reduction in the rate of vulcanization at 227? F., between Stock No. 1 and 2 or 3, which contain a retardant. The rate of vulcanization in the cure at 227 F. is indicative of the tendency of the stock to pre-vulcanize at processing temperatures.

. The modulus and tensile strength shown by Stock No.1 are high enough to indicate the danger of pro-vulcanization during processing The modulus and tensile strength shown by Stock No. 2 or am sufficiently low to indicate processing safety.

' Z Another method of determining the emciency of a retarder is the so-called stability test conducted at 120 F., in which the time necessaryfor I the stock to pre-vulcanize is determined. In performing this test the uncured stock is stored in an oven at 1209;. At frequent intervals portions of the stock areremoved and milled on an ordinary rubber mill to form a smooth sheet. When the aged stock has pre vulcanized to such an extentthat it can no longer be milled to a smooth sheet-,it is said to be set up." From the data shown in the above table it can be seen that sodium acetate markedly improves the stability of neoprene stocks.

In the cure at 274 F. it is shown that these 7 materials do not retard the rate of vulcanization,

butproduce a slight activating effect, as shown by the increase in modulus at 600% elongation. It ischaracteristic of neoprene stocks, in which the rate of vulcanization has been increased, to show a slight increase in hardness, a somewhat lower elongation at break, and consequently a somewhat lower tensile strength. This efiect is shown by Stocks Nos. 2 and 3..

In orderto illustrate the advantages obtainable by the use of these retardantswith a recently prepared neoprene, the following stocks were tested, in each case the neoprene being the same as employed in the examples of Table II.

Table III Stock Neoprene 100. 0 100. 0 100.0 100. 0 100. 0 Pbenyl alpha napbthylamina. l. 0 1. 0 1. 0 1. 0 1.0 Extra light calcined magnesia 4. 0 4. 0 .4. 0 4. 0 4. 0 Ghannel carbon black 10. 0 10. 0 l0. 0 10.0 10.0 10 Zinc oxide. 5. 0 5. 0 5. 0 5.0 5. 0 Sodium acetat 1. 0 Zinc acetate 1.0 Iron acetate. l. 0 acetate 1.0

1 CURE: 60 MIN. AT 227 F.

Modulus at 600%, lbsJsq. in. 75 N N N Tensile strength, lbs/sq. in. 550 0 o O NO Elongation at break, per cent 1, 280 cure cure cute cute CURE: 60 MIN. AT 274 F.

Modulus at 600%, lbs/sq. in. 1,450 l, 825 l, 450 1,425 l, 500 Tensile strength, lbs/sq. in 3, 900 3, 700 3, 625 4, 025 3, 650 Elongation at break, per cent. 925 835 880 895 840 Hardness (Shore) 49 50 52 50 52 In Table III it can be seen that various metallic salts of acetic acid have a pronounced retarding effect on the rate of vulcanization in the cure at 227 F. It is plainly seen that these metallic 3o salts do not retard the rate of vulcanization in the cure at 274 F.

For many commercial uses it is desirable to employ organic accelerators in the vulcanization of "neoprene. We have found that the retarders of our invention are also effective in the presence of an organic accelerator. In order to illustrate this fact the following tests were made.

Parazone (para phenyl phenol), a very mild accelerator which is used to increase heat resistance yet tends to produce stocks which are ."scorchy, was tested with various retarders as follows, the neoprene being the same as employed in Table II.

Table IV Stock Neoprene; 100.0 100.0 100.0 Phenylalphanaphthylaminenfl l. 0 l. 0 1. 0 'Parazone 1.0 1.0 1.0 Extra light calcined magnes 4. 0 4. 0 4. 0 Channel carbon black 10.0 10.0 10.0 Zinc oxide 5.0 5.0 5.0

P0tassium formate; 1.0 Sodium acetate. 1.0

CURE: MINI 'AT 227 F.

Modulus at 600%, lbs/sq. in Tensile strength, lbs/sq. in...

Hardness (shore) In Table IV it can be seen that a metallic salt of either formic or acetic acid shows a pronounced retarding effect on the rate of vulcanization of neoprene in the cure at 227 F., in the presence of Parazone, In the cure at 274 F. these metallic salts do not retard the rate of vulcanization.

, From a practical standpoint some stearic acid is normallyused in neoprene as a lubricating lessthan 1.(l 10- 11 by sodium acetate naphthoquinone. r

The retarding efi'ect produced by these materials is not restricted to the vulcanization of neoin conjunction with beta preferred salt for retardin neoprene artificial rubber of these acids are the alka The preferred salts 1i metal, ammonium prene of a particular type. We have-found that 5 and substituted ammonium salts. this retarding efiect is also observed in various The metalhc salts of the acids of the type above types of chloro-2-butadiene-1,3 polymers. To ilmentioned may be employed either alone or in lustrate this, the following stocks weretested. conjunction with organic accelerators. It is, of

Table X Stock Neoprene 100.0 100.0 100.0 100.0 Neoprene 100. 0 100. 0 Neoprene I. 100. 0 100. 0 100. 0 100. 0 Stem-i0 acid 2.0 2.0 2.0 ,2.0 2.0 2.0 a 2.0 2.0 2.0 2.0 Pheuyl alpha naphthylamine..- 1.0 1.0 v 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

erazone 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Extra 11 ht calcined magnesia.--" 10.0 10.0 10. 0 10. 0 5.0 5. 0 10.0 10. 0 10.0 10.0 Channe f oarbon black.- 10.0 10.0 10.0 10.0 11.0 11.0 10.0 10.0 10.0 10.0 Zinc oxide 10.0 10.0 10.0 10.0 5.0 5.0 10.0 10.0 10.0 10.0 sulrur 5 5 0 5 0 1.0 1.0 FF wood rosin 0 s di Me 1.0 1.0 1.0 1 0 1.0 Pearm f ni 1.0 1 .0 1.0 1.0

Neo rene re ared accordin to the method described in U. S. P. 2,259 122 Example No. 16. 1 N eogreue sugared according to the method described in Example 1 of Br tish Patent 673,024.

' Neoprene prepared according to the method described in U. 8. Patent 2,395,649.

' CURE: 00 MIN. 11'1- 227 F. v

Modulus at 000 575 500 1 250 025 925 000 425 1 000 350 Tensile strength? 2,200 1, 450 21100 1,825 1,000 025 1, 350 000- 050 2,350 Elongation at break, percent. 1,210 1,185 880 1, 120 780 840 1,000 1,030 860 960 CURE: 00 MIN. AT 274 F.

Mdul t "1475 1215 2050 1800 .-1025 2,025 2,225 2,25 're isile s tr en gt lf i I950 2:700 21000 21015 000 050 3:225 3,200 3,250 a, 125 Elongation at break, peroent.- 860 850 680 710 250 240 760 740 740 Hardness (Shore) 48 50 51 51 52 54 54 55 5 I s illustrated in the above tables, the retarding efiect produced by sodium acetate and related compounds takes place in neoprene of various types so that the invention is applicable in preventing premature curing of polymerized chloro-2-butadiene-1,3 itself or when it is modified by copolymerization or interpolymeriz'ation with other materials that may be polymerized therewith to change the characteristics of the resulting rubber-like material- While in the above examples a relatively small number of metallic salts boxylic acids having a dissociation constant of ave been mentioned, it is to be understood that these examples are given merely to illustrate the invention, and that the invention is not limited to the use of these particular compounds. As furtherillustrative of the type of salts that may be employed are alkali metal or ammonium salts of the more commonly known aliphatic acids such as propionic'acid, butyric acid, valeric acid; capric acid, heptoic acid, Pelargonic acid, lauric acid, stearic acid, crotonic acid, oleic acid, propiolic acid, sorbic acid, linoleic acid, glycolic acid, and lactic acid, beta hydroxy propionic acid, and the aromatib acids of the'benzene and naphthalene series such as alpha-naphthoic. acid, beta-naphthoic acid, benzoic acid, etc. For the purpose of this invention the use of the aliphatic acids, particularly those otherwise unsubstituted aliphatic acids that contain only C and H in the alkyl chain is preferred, and more particularly those of lower molecular weight, of. from 1 to 7 carbon atoms. Because 01 its ailability and relatively low price and because of the efliciency with which of organic mono-care vulcamzing at processi course, obvious that compounding ingredients and fillers other than those mentioned in the above tables may be employed, and in different proportions.

The amount of retarders when used either alone or in conjunction with organic accelerators will usually comprise from about 0.10 part to 10 parts for every parts of polymerized chloro- 2-butadiene-1,3, and preferably from about 0.50 part to 4.0 parts.

Use of these metallic salts produces neoprene stocks which are safe from premature curing or 11g temperatures, yet which aracteristics at normal curing temperatures, the resulting vulcanizates exhibiting exceedingly deterioration by heat ance to tear and 1111 We claim '1. A vulcanizable com merized chloro 2 bu timately incorporated retain their curing ch or oxidation, good resistproved resiliency.

position comprising polytadiene- 1,3, having intherein zinc oxide and magnesium oxide in suflicient amounts to eflect vulcanization of thelpolymerized chloro-2-butadiene-1,3 at vulcanizing temperatures, and from 0.10 to 10 parts of a metallic salt of an organic mono-carboxylic acid per 100 parts of the polymerized chloro-2-butadiene-l,3, which acid has a dissociation constant less than 1.0 10- 2. A vulcanizable composition comprising polymerized chloro-2-butadiene ly incorporated therein zinc oxide and magnesium oxide in suflicient amounts to elfect vulcanization of the polymerized ch1or0-2-butadiene-1,3 at vulcanizing temperatures, and from 0.10 to 10 parts of a sodium salt of an organic mono-carboxylic er, sodium acetate is the g the vulcanization. of

ood resistance toward -1,3, having intimatearoasez acid per 100 parts or the polymerized chloro-2- butadiene-LB, which acid has a dissociation constant less than toxic- 3. A vulcanizable composition comprising polymerized chloro-2-butadiene-l,3, having intimate- 1y incorporated therein zinc oxide and magnesium oxide in sumcient amounts to effect vulcanization of the polymerized 'chloro-2-butadiene-L3'at vulcanizing temperatures, and from 0.10 to 10 parts of sodium acetate per 100 parts of the polymerized chloro-2-butadiene-1,3.

4. A composition comprising polymerized chloro 2 butadiene 1,3 having incorporated therein prior to vulcanization zinc oxide, magnes'ium oxide and from 0.19 to l parts of a metallic salt of an organic mono-carboxylic acid per 100 parts of the polymerized chloro-2-butadime-1,3, which acid has a dissociation constant lessthan1.0 l0- V v 5. Vulcanized polymerized chlQrO-Z-butadiene- 1,3 having incorporated therein prior to vulcanization zinc oxide, magnesium oxide and from 0.10 to 10 parts of an alkali metal salt of an organic mono-carboxylic acid perlOO parts of the polymerlzed chloro-2-butadiene-L3, which acid has a dissociation constant less than 1.0 10- 6. Vulcanized polymerized chloro-z-butadiene- 1,3 having incorporated therein prior to vulcaniene-l,3- having incorporated therein prior to vulcanization zinc oxide, magnesium oxide and from 0.10 to 10 parts or an alkali metal salt of an aromatic mono carboxylic acid of the benzene and merized chloro-2-butadiene-L3,

12. A vulcanizable composition comprising polymerized chloro-2-butadiene-1,3 having intimate- 1y incorporated therein zinc oxide and magnesium oxidein suificient amounts .to effect vulcanization of the chloro-2-butadiene-l,3 at vulcanizing temperatures, and from 0.10 to 10 parts of an alkali metal salt or an organic monocarboxylic acid per 100 parts of the polymerized ohloro-2- butadiene-l,3, which acid has a dissociation constant less than 1.0xl0 V 13. A vulcanizable composition comprising polymerized chloro-2-butadiene-1,3 having intimately incorporated therein zinc oxide and magnesium oxide in suficient amounts to efiect vulcanization of the chloro-2-butadiene-1,3 at vulcanizing temperatures, andirom 0.10 to 10 parts zation zinc oxide, magnesium oxide and from 0.10

to lOparts of a sodium salt of an organic monocarboxylic acid per 100 parts of the polymerized chloro-2-butadiene-L3, which acid has a dissociation constant less than 1.0Xl0- 'I. Vulcanized polymerized chloro-Z-butadiene- 1,3 having incorporated therein prior to vulcanization zinc oxide, magnesium oxide and from 0.10 to 10'parts of an alkali metalsalt of an aliphatic .mono-carboxylic acid per 100 parts of the polym'rized chloro-2-butadiene-1,3 which acid has a dissociation constant less than 1.0 10- 8. Vulcanized polymerized chloro-2-butadiene- 1,3 having incorporated therein prior to vulcanization zinc oxide, magnesium oxide and from 0.10 to 10 parts of an alkali metal salt of an aliphatic monocarboxylic acid containing only H and C in an alkyl chain, per 100 parts of the polymerized chloro-2-butadiene- 1,3, which acid has a dissociation constant less than 1.0x ill- 9. Vulcanized polymerizedchloro-2-butadiene- 1,3 having incorporated therein prior to vulcanization zinc oxide, magnesium oxide and from 0.10 to 10 parts. of an alkali metal salt of an aliphatic mono-carboxylic acid containing from 1 to 7 carbon atoms and containing only H and C in an of an alkali metal salt of an aliphatic monocarboxylic acid per parts of the polymerized chloro-Z-butadlene-LB, which acid has a dissociation constant less than 1.0 X ill-' 14. A vulcanizahle composition comprising polymerized chloro-2-'butadiene-1,3 having intimately incorporated therein zinc oxide and magnesium oxide in sufficient amounts to efiect vulcanization of the chloro-2-butadiene-L3 at vulcanizing temperatures, and from 0.10 to 10 parts 01 an alkali metal salt of an aliphatic monocarboxylic acid,

containing only H and C in an alkyl chain, per

100 parts of the polymerized chloro-Z-butadiene- 1,3 which acid has a, dissociation constant less than 1.0 x 10 15. A vulcanizable composition comprising polymerized chloro-2-butadiene-l,3 having intimately incorporated therein zinc oxide and magnesium oxide in suflicient amounts to effect vulcanization of the chloro-2-butadiene-L3 at vulcanizing temperatures, and from 0.10 to 10 parts of an' alkali metal salt of an aliphatic monoearboxylic acid. containing from 1 to 7 carbon atoms and containing only H and C in an alkyl chain, per 100 parts of the polymerized chloro-2-butadiene-l,3, which acid has a dissociation constant less than 1.0 X 10- 16. A vulcanizable composition comprising polymerized chloro-2 -butadiene-l,3 having intimately incorporated therein zinc oxide and magnesium oxide in sufficient amounts to effect vulcanization of the chloro-2-butadiene- 1,3 at Vulcanizing temperatures, and from 0.10 to 10 parts of an alkali metal salt of an aromatic monocarboxylic acid of the benzene and naphthalene series per 100 parts of the polymerized chloro-2-butadiene-l,3, which acid has a dissociation constant less than 1.0 10- JAMES P. NOWLEN.

MAYNARD F. TORRENCE.

naphthalene series per 100 parts of the poly- 

